Answer : 3. "Hawa Mahal"
Explanation :

1. Hawa Mahal of Jaipur was built by Sawai Pratap Singh.

2. Hawa Mahal is a five-storey palace, made of red and pink sandstone.

3. The famous 'Palace of the Winds', or Hawa Mahal, is one of the major tourist attractions in the city of Jaipur.

4. Apart from this, due to the "Venturi effect", cool air always keeps coming inside the palace through these intricately structured lattice windows, due to which the palace always remains air-conditioned even in the scorching heat.